Friction stir bonding method

ABSTRACT

The end of a face plate  11  of a hollow member  10  is abutted against the end of a face plate of a hollow member  20 . The end of a face plate  21  is stacked to a protrusion  15 . A small-diameter portion  52  of a rotary tool  50  is inserted to the abutted area, and the tool  50  is moved along the abutted region while being rotated in the right direction observed from the large-diameter portion  51 . The direction of movement is from the front of the drawing of FIG.  1  toward the far end thereof. In FIG.  1 , the pressure of mobilized metal is greater in the right side of the axial center of the rotary tool. The thickness of the member from the tip of the inserted small-diameter portion  51  to the hollow areas  10   b  and  10   a  is thicker at the right side. Accordingly, the thickness of the member is greater at the right side of the tool where the pressure is higher, thus preventing metal from flowing out into the hollow region  10   a . Since the member positioned to the left side of the tool is thinner, the weight of the bonded member is reduced.

FIELD OF THE INVENTION

[0001] The present invention relates to a friction stir bonding method,and is especially preferable for application to bonding hollow members.

DESCRIPTION OF THE RELATED ART

[0002] A friction stir bonding method is a method for bonding members byinserting a round shaft (called a rotary tool) to a joint portion andmoving the tool along the joint line, thereby heating, mobilizing andplasticising the joint portion in order to perform solid-phase bondingof the members. The rotary tool comprises a large-diameter portion and asmall-diameter portion. The small-diameter portion is to be inserted tothe members to be bonded, and the end surface of the large-diameterportion contacts the members. The small-diameter portion is equippedwith a screw.

[0003] Moreover, a convex portion is formed to the area where the rotarytool is to be inserted between the two members to be bonded, and themetal material forming the convex portion is mobilized to fill the gapbetween the two members. The large-diameter portion of the rotary toolis arranged to fit within the convex portion.

[0004] Since the rotary tool must be inserted to the metal of the jointportion, great force is applied to the joint portion. Therefore, whenbonding hollow members, the portion of a connecting plate connecting thetwo face plates of a hollow member is positioned at thefriction-stir-bonding position between another hollow member. Thefriction stir bonding is carried out while the connecting plate receivesthe force applied to the joint, and therefore, deformation of the hollowmembers is prevented.

[0005] These methods are disclosed in Japanese Patent Laid-OpenPublication No. 11-90655 (U.S. Pat. No. 6,050,474).

SUMMARY OF THE INVENTION

[0006] Friction stir bonding is carried out by inserting a rotary toolto the members to be bonded, thereby plasticising and mobilizing themetal material thereof. If the thickness of the material from the tipportion of the small-diameter portion of the inserted rotary tool to theback surface of the bonded member (opposite to the large-diameterportion) is small, the mobilized metal may flow out to the back surfacethereof. Even if the material does not flow out, the member will beexpanded outwardly. Such phenomenon is also included in the meaning ofthe term “flow-out” used hereinafter in the specification. Because ofthis flow-out, the thickness of the protrusion compensating for theflow-out metal material must be increased. The flow-out also causesholes to be generated to the joint portion. In an attempt to prevent theflow-out, the thickness of the member is increased so that the distancefrom the tip of the small-diameter portion to the back surface of themember is increased. However, this increases both the weight of themember and the manufacturing cost thereof.

[0007] The object of the present invention is to provide a friction stirbonding method enabling a lightweight bond having good characteristics.

[0008] Based on various studies related to friction stir bonding, it isnow discovered that the pressure of the metal mobilized by the rotationof the rotary tool is not even within the range of influence of therotary tool to the axial direction, but the pressure is differentaccording to position. It is considered that the position receivinghigher pressure is determined by the direction of rotation of the rotarytool and the direction of movement of the tool.

[0009] The friction stir bonding method according to the presentinvention characterizes in positioning the portion of the member havinggreater thickness, from the tip of the small-diameter portion to theback surface of the member, where the mobilized metal has the greatestpressure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a vertical cross-sectional view showing the jointportion according to one embodiment of the present invention;

[0011]FIG. 2 is a plan view of FIG. 1;

[0012]FIG. 3 is a vertical cross-sectional view showing one pair ofhollow members according to one embodiment of the present invention;

[0013]FIG. 4 is a perspective view showing the body of the railroad car;and

[0014]FIG. 5 is a vertical cross-sectional view showing the jointportion according to another embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0015] One embodiment of the present invention will now be explainedwith reference to FIGS. 1 through 4. A body 500 of a railroad carcomprises a side structure 501 constituting the side surfaces, a roofstructure 502 constituting the roof, an underframe 503 constituting thefloor, and an end structure 504 constituting the longitudinal edgeportions of the car. The side structure 501, the roof structure 502 andthe underframe 504 are each formed by bonding plural extruded members10, 20. The longitudinal direction (the extruded direction) of theextruded members 10, 20 are arranged to the longitudinal direction ofthe car body 500. The extruded members 10, 20 are hollow members made ofaluminum alloy.

[0016] The structure of the hollow members 10, 20 constituting the sidestructure 501 will now be explained. The hollow members constituting theother areas are similarly formed.

[0017] The hollow member 10 (20) comprises two substantially parallelface plates 11 (21), 12 (22), and a plural number of connecting plates13 (23) connecting the two face plates. The connecting plates 13 (23)are each tilted against the face plates 11 (21) and 12 (22). In otherwords, the face plates 11 (21), 12 (22) and the connecting plates 13(23) constitute a truss.

[0018] A connecting plate 14 (24) formed to the end portion of thehollow member 10 (20) in the width direction is orthogonal to the faceplates 11, 12 (21, 22). The outer surface of the joint between theconnecting plate 14 and the face plate 11 (12) is a convex portion forreceiving the face plate 21 (22) of the hollow member 20. The endportion of the hollow member 10 is stacked on the face plates 21, 22 ofthe hollow member 20. The ends of the face plates 11, 12 are eachprovided with a protrusion 15 for supporting the face plate 21 or 22.The protrusion 15 is protruded from the connecting plate 14. Theprotrusion 15 is connected to the concave portion.

[0019] The end of the face plates 11, 12 (21, 22) are each provided witha convex portion 17 (27) extending outward from the outer surface of thehollow members 10, 20 (protruded outward in the direction of thickness).The end surface of the face plates 11, 21 (21, 22) and the convexportion 17 (27) is formed along the direction of thickness of the hollowmember 10 (20). The end surface of the face plates 11, 21 and the convexportion 17 (in other words, the convex portion close to the face plates11, 12) is positioned near the center of thickness of the connectingplate 14. The end surface of the face plate 11 (12) and the convexportion 17 of the hollow member 10 is abutted against the end surface ofthe face plate 21 (22) and the convex portion 27 of the hollow member20.

[0020] The face plate 11 (12) and the face plate 21 (22) are positionedalong the same face, and the protruded margin of the convex portions 17and 27 are equal. The width of the two convex portions 17, 27 are equal.The width of the two convex portions is greater than the diameter of thelarge-diameter portion 51 of the rotary tool 50. The metal forming theconvex portions 17, 27 is used as the source material for filling thegap of the abutted portions.

[0021] Upon bonding, the two hollow members 10, 20 are fixed on a base100. Reference number 101 refers to a groove to which the convexportions 17, 27 formed to the lower surface is inserted.

[0022] The rotary tool 50 comprises a large-diameter portion 51 and asmall-diameter portion 52 mounted on the end of the large-diameterportion 51. The small-diameter portion 52 is equipped with a screw. Uponbonding, the rotary tool 50 is inserted to the abutted portions. Thebottom area of the large-diameter portion 51 is positioned within theconvex portions 17, 27. The small-diameter portion 52 is inserted to theabutted portions between the face plates 11 and 21. The lower end of thesmall-diameter portion 52 is somewhat inserted to the protrusion 15.While rotating the rotary tool 50, the tool is moved along the jointline of the abutted portions.

[0023] After inserting the rotary tool 50 to the area to be bonded, therotary tool 50 is moved from the closer side of the drawing of FIG. 1 tothe farther side thereof. In FIG. 2, which is a plan view of FIG. 1,arrow A shows the direction of movement of the rotary tool 50, and arrowB shows the direction of rotation of the rotary tool 50. The screw ofthe small-diameter portion 52 is a left-hand screw. When observing thesmall-diameter portion 52 from the large-diameter portion 51, therotational direction of the rotary tool 50 is rightward (clockwise).When looking forward from the rotary tool 50 toward the direction ofmovement, the protrusion 15 is positioned to the right from the centerof axis of the rotary tool 50, as shown in FIG. 1.

[0024] After the friction stir bonding of the upper surface shown inFIG. 3 is finished, the hollow members 10, 20 are reversed, and frictionstir bonding is similarly performed to the other side.

[0025] The pressure provided to the metal material of the joint portionmobilized by the rotary tool 50 is greater in the right side of theaxial center of the rotary tool 50 than the left side thereof in thedirection of movement of the rotary tool 50. The right-hand rotation ofthe rotary tool 50 is considered to cause this phenomenon, the rotationpushing the material existing in front of the rotary tool 50 that hasnot yet been bonded toward the right side of the tool.

[0026] In FIG. 1, a hollow area 10 b, 10 a exists on the left and rightsides of the connecting plate 14. The distance from the tip of thesmall-diameter portion 15 inserted to the joint portion to the left andright hollow areas 10 b, 10 a is set so that the distance from the tipto the protrusion 15 existing in the right side is greater than to theleft side. Since the protrusion 15 must support the face plate 21, thethickness of the protrusion is relatively thick. Therefore, thethickness of the area of the member receiving higher pressure isdesigned thicker. The mobilized metal will not flow out into the hollowarea 10 a because of this thickness of the protrusion 15, and therefore,no hole will be generated within the joint portion.

[0027] On the other hand, the pressure provided to the left side of therotary tool 50 is relatively low compared to the right side thereof. Thereason for this is considered to be because no unbonded metal existsbehind the rotary tool 50.

[0028] Since the left side of the axial center of the rotary toolreceives small inner pressure, the thickness of the member measured fromthe tip of the small-diameter portion 52 to the hollow portion 10 b ofthe left side of the connecting plate 13 can be reduced. This enables tolighten the weight of the hollow member 10.

[0029] The “thickness of the member beginning from the tip of theinserted small-diameter portion 52 to the hollow portions 10 b or 10 a”will now be explained with reference to FIG. 1. The thickness of themetal needed in order to prevent the flow-out of metal at the sidereceiving higher pressure is set as R. Thickness R is necessary t theright side of the axial center of the small-diameter portion 52 measuredfrom the tip of the portion 52. In other words, the member on the rightof the small-diameter portion 52 must have a thickness of radius Rcentering at the right-end corner of portion 52. The term “thickness ofthe member beginning from the tip of the inserted small-diameter portion52 to the hollow portion lob” refers to the thickness in the horizontaldirection as well. The thickness of the member to the left of the axialcenter of the small-diameter portion 52 is smaller than thickness R.

[0030] We will now consider a comparison example, where the direction ofthe screw and the rotating direction of the rotary tool 50 is the sameas the above-mentioned embodiment, but the position of the hollowmembers 10 and 20 are opposite, or in other words, the protrusion 15 isprotruded toward the left side of the rotary tool 50. In this case, thethinner member is positioned to the right side of the rotary tool 50where the pressure is higher, so the mobilized metal material flows outinto the hollow space. Therefore, a hole may be generated within thejoint portion.

[0031] Moreover, when the stacked area of the protrusion 15 and the faceplate 21 are placed to the left side of the small-diameter portion, thestacked surface near the joint portion may be knuckled toward thelarge-diameter portion 51 of the rotary tool 50, generating a notch.However, if the stacked area is positioned to the right side thereof,the stacked area exists where the pressure is high, and thereforereduces the possibility of generating a notch.

[0032] In other words, the area having a greater thickness measured fromthe tip of the small-diameter portion 52 to the surface of the memberopposite the large-diameter portion 51 should be placed where thepressure is higher. The high-pressure region exists at the right side ofthe rotary tool 50 when observing the tool from behind the direction ofmovement, if the direction of rotation of the rotary tool 50 isright-hand rotation when observing the tool from the large-diameterportion 41.

[0033] If the screw of the small-diameter portion 52 is a right-handscrew, and if the direction of rotation of the rotary tool 50 isleft-handed (counterclockwise), the hollow members 10 and 20 should beoppositely assembled, so that the protrusion 15 is positioned to theleft of the axial center of the rotary tool 50.

[0034]FIG. 5 shows the present bonding method applied to bond non-hollowmembers. The face plates 12, 22 and connecting plates 14, 24 are removedfrom the hollow members 10 and 20 of FIG. 2. The back surface of thejoint portion is mounted on a flat base 105.

[0035] The technical scope of the present invention is not limited tothe terms used in the claims or in the summary of the present invention,but is extended to the range in which a person skilled in the art couldeasily substitute based on the present disclosure.

[0036] According to the friction stir bonding of the present invention,a lightweight bond having good characteristics is provided.

We claim:
 1. A friction stir bonding method for bonding a first memberand a second member, the first member comprising a plate and aprotrusion protruding substantially parallel to said plate from the endportion of said plate and arranged at a retreated position from onesurface of said plate, said friction stir bonding method comprising thesteps of: superimposing the end portion of said second member on saidprotrusion, and abutting said end portion of said second member againstthe end portion of said plate; and friction stir bonding the abuttedportions using a rotary tool having a small-diameter portion mounted onthe end of a large-diameter portion, by inserting said small-diameterportion to said abutted portions; wherein the rotary tool is positionedso that when observed from the direction from which said tool movesalong said abutted portions, the distance from the tip portion of saidinserted small-diameter portion to the surface of said first memberopposite from said large-diameter portion is greater in the right sideof the axial center of said rotary tool than the left side thereof; andsaid rotary tool is rotated in the right direction when observed fromthe large-diameter portion side while being moved along said abuttedportions.
 2. A friction stir bonding method according to claim 1,wherein said protrusion is positioned to said right side when performingsaid friction stir bonding.
 3. A friction stir bonding method accordingto claim 1 wherein the tip portion of said small-diameter portion isinserted to said protrusion when performing said friction stir bonding.4. A friction stir bonding method for bonding a hollow member comprisingtwo substantially parallel face plates, a connecting plate forconnecting said two face plates, a protrusion protruding substantiallyparallel to one face plate from said connecting plate, and a concaveportion recessed both from the outer side of said one face plate andfrom the protruded direction of said protrusion at the joint portionjoining said one face plate, said connecting plate and said protrusion;said friction stir bonding method comprising the steps of: superimposingthe end portion of a second member on said concave portion, and abuttingsaid end portion of said second member against the end portion of saidone face plate; and friction stir bonding the abutted portions using arotary tool having a small-diameter portion mounted on the end of alarge-diameter portion, by inserting said small-diameter portion to saidabutted portions and said protrusion; wherein said protrusion ispositioned to the right side of the axial center of said rotary toolwhen said rotary tool is observed from the direction from which saidtool moves along said abutted portions; the distance from the tipportion of said inserted small-diameter portion to the surface of saidhollow member opposite from said large-diameter portion is greater inthe right side of the axial center of said rotary tool having saidprotrusion than the left side thereof, when observed from the directionfrom which said tool moves; and said rotary tool is rotated in the rightdirection when observed from the large-diameter portion side while beingmoved along said abutted portions.
 5. A friction stir bonding method forbonding a first member and a second member, the first member comprisinga plate and a protrusion protruding substantially parallel to said platefrom the end portion of said plate and arranged at a retreated positionfrom one surface of said plate, said friction stir bonding methodcomprising the steps of: superimposing the end portion of said secondmember on said protrusion, and abutting said end portion of said secondmember against the end portion of said plate; and friction stir bondingthe abutted portions using a rotary tool having a small-diameter portionmounted on the end of a large-diameter portion, by inserting saidsmall-diameter portion to said abutted portions; wherein the rotary toolis positioned so that when observed from the direction from which saidtool moves along said abutted portions, the distance from the tipportion of said inserted small-diameter portion to the surface of saidfirst member opposite from said large-diameter portion is greater in theleft side of the axial center of said rotary tool than the right sidethereof; and said rotary tool is rotated in the left direction whenobserved from the large-diameter portion side while being moved alongsaid abutted portions.
 6. A friction stir bonding method according toclaim 5 wherein said protrusion is positioned to said left side whenperforming said friction stir bonding.
 7. A friction stir bonding methodaccording to claim 5, wherein the tip portion of said small-diameterportion is inserted to said protrusion when performing said frictionstir bonding.
 8. A friction stir bonding method for bonding a hollowmember comprising two substantially parallel face plates, a connectingplate for connecting said two face plates, a protrusion protrudingsubstantially parallel to one face plate from said connecting plate, anda concave portion recessed both from the outer side of said one faceplate and from the protruded direction of said protrusion at the jointportion joining said one face plate, said connecting plate and saidprotrusion; said friction stir bonding method comprising the steps of:superimposing the end portion of a second member on said concaveportion, and abutting said end portion of said second member against theend portion of said one face plate; and friction stir bonding theabutted portions using a rotary tool having a small-diameter portionmounted on the end of a large-diameter portion, by inserting saidsmall-diameter portion to said abutted portions and said protrusion;wherein said protrusion is positioned to the left side of the axialcenter of said rotary tool when said rotary tool is observed from thedirection from which said tool moves along said abutted portions; thedistance from the tip portion of said inserted small-diameter portion tothe surface of said hollow member opposite from said large-diameterportion is greater in the left side of the axial center of said rotarytool having said protrusion than the right side thereof, when observedfrom the direction from which said tool moves; and said rotary tool isrotated in the left direction when observed from the large-diameterportion side while being moved along said abutted portions.